Neighboring plants can influence the amount of herbivory that a focal plant receives. The most commonly studied mechanisms for these “associational effects” involve effects of neighboring plants on herbivore behavior, such as neighboring plants repelling herbivores with volatiles. However, another mechanism that may drive associational effects is the impact of neighbor species on a focal plant’s trait expression. In a field experiment using Solanum carolinense as a focal species, we quantified the effects of 11 common old-field neighbor species on three plastic traits important to plant interactions with herbivores: specific leaf area (SLA), trichome density, and leaf toughness. Six genotypes of S. carolinense were grown in plots with nine individuals of a single neighboring plant species (n=6 replicate plots) throughout an entire growing season. We collected one leaf from each S. carolinense at the end of the season and used it to calculate SLA, trichome density, and toughness. We used a Winn penetrometer to measure leaf toughness immediately after collection; the mass and area of each dried leaf were used to determine SLA; and we calculated trichome density by counting the number of trichomes in a 12.5 mm2 circle.
Results/Conclusions
Specific leaf area and leaf toughness of S. carolinense differed significantly with neighbor species. Neighboring plant species had no significant effect on trichome density. Both specific leaf area and trichome density also differed significantly among genotypes of S. carolinense. Our results indicate that the expression of some traits that are important to interactions with herbivores may be influenced by neighboring species identity while others are not. Our findings suggest that neighboring plants may impact the mean and variance of intraspecific trait variation among plants, making individuals more or less susceptible to herbivory, and changing the distribution of trait values within populations.